Pierre-Francois-Andre Mechain and Jean-Baptiste-Joseph Delambre——in addition to their names implying equally indecisive parents——spent the years 1791-1799 measuring the length of the Earth’s arc between Dunkirk, France and Barcelona, Spain. They endured the hardships you would expect of late-18th-century travel including imprisonment by skeptical townspeople. By measuring this arc, the pair hoped to calculate the distance from the North Pole to the Equator, allowing them to standardize the meter as 1/10,000,000 of this span.
It was a noble goal: relating all lengths to this meter would define all distances based on their ratio to the Earth—a natural system of measurement!
Unfortunately, they blew the calculations. Mssrs. Mechain and Delambre forgot to adjust for oblateness—the Earth is not a perfect sphere as they assumed in their calculations; it’s flattened at the poles. And the Earth itself isn’t uniform; it’s lumpy. So each meridian is, in fact, a different length.
Other metric measurements are based on the flawed meter, with the liter defined as a cube with sides of 0.1 meter, and the kilogram as the mass of a liter of water at maximum density. Thus, while overall the metric systems sucks much less than the system of English units, the metric system remains measurement based on human rather than natural definition.
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